Presently there exist various designs of magnifying spectacles of the type in which a magnifying lens system is arranged in front of each eye of the user, the lens system preferably being designed in the manner of a Galilean telescope. The magnifying lens system may be either mounted separately in a frame for attachment to spectacles, or more advantageously may be combined with corrective lenses of a pair of spectacles. In some of such systems, the magnifying lenses are attached to a support in a position of convergence corresponding to the working sight distance, the support itself being attached to the bridge of the eyeglass frame. In other systems of this type, the magnifying lens systems are directly joined to the corrective lenses of the spectacles, such as by cementing a holding ring to the corrective lens or mounting the telescope in a through-opening provided in the lens for receiving the scope.
Such magnifying spectacles are useful where magnified, sharp, critical, prolonged and comfortable vision is required, as for example in surgery, dental work, dermatological work and in the assembly of miniature parts. Small telemicroscopes mounted to the lenses of otherwise conventional spectacles have also proven helpful to individuals who suffer low vision The term telemicroscopes is intended to include both instruments used to make distant objects appear nearer, and thus larger (telescopes), and instruments used to make near objects appear larger (microscopes). Examples of particular telemicroscopic arrangements which have been used by low vision individuals, as well as by the normally sighted for special work applications are to be found in the U.S. Edwards Pat. No. 4,540,238 and in the patents cited as references therein, as well as in the Pekar et al U.S. Pat. No. 4,704,000 and the patents cited as references therein.
The bilevel telemicroscopic apparatus of the aforementioned Edwards '238 patent is considered advantageous in providing light weight telemicroscopic spectacles which, to the casual observer, appear to be completely conventional while providing a significant depth of view and a bilevel vision effect. The Edwards telemicroscopic spectacles accomplish this by directly mounting the telemicroscopes fixedly and permanently into the spectacle lenses so as to extend rearwardly therefrom toward the wearer's eyes, but not so as to protrude forwardly beyond flush with the front or outer surface of carrier lenses. The telemicroscope is miniaturized in order to fit in the small space between the cornea of the eye of the wearer and the eyeglass lens. The scope is either adhesively attached to the rear surface of the carrier lens or fixedly mounted in a through opening in the carrier lens so that the front surface of positive element of the scope rests flush with the front surface of the carrier lens. In either event, the negative element of the scope is positioned no closer than eye lash length from the eye ball.
The Edwards telemicroscopes are adjustable by a screw connection of the positive and negative lenses so that special prescriptions are not required. The short length of the telemicroscope lens contributes to a significant field of view of the scope. Due to its miniature size, the telemicroscope can be positioned with one edge at about the eyes central viewing axis. Thus, with a scope having an outer diameter of less than 10 mm as described above, and with the optic axis of the scope within 5 mm of the eye's central viewing access, bilevel vision is thereby made possible. In bilevel vision, the patient observes the regular field of view and the smaller magnifying field of use simultaneously with no confusion. With the bilevel effect, the patient need not focus first on the regular view and then the magnifying view; both views are continuously apparent to him.
However with the aforementioned Edwards telemicroscope-equipped spectacles, as well as with other prior art magnifying spectacles, the magnifying lens system must be adjusted relative to the pair of eyes and to each other in a manner such that the axes of the system coincide with the lines of vision of the pair of eyes to an object point disposed on the focal plane of the magnifying lens system. In magnifying spectacles in which the magnifying lens systems are directly joined to the spectacle corrective lenses, particularly when permanently mounted interiorly to or rearwardly of the lenses as in the aforementioned Edwards patent system, such adjustment offers some difficulties. Although the scopes are adjustable in focus by screw threaded telescopic mounts of the front and rear lenses, such focus adjustment cannot be done by the user himself while wearing the spectacles in normal position due to the inaccessability of the scopes disposed in the limited space between the corrective lenses and the eye balls of the user. Accordingly, adjustment must be done with the eyeglasses removed, then the same refitted and the focus adjustment checked, and so on through a trial and error iteration process. Preferably such focus fitting is done by the attending optician, and hence accurate adjustment of the magnifying lens system is rendered even more difficult because the optician is not able to effect the adjustment from his own view, but only according to the statements made by the user.
In addition, such permanent scope mounting employed in prior art telemicroscopes renders the fitted scope-lens unsuitable for making later centering readjustments laterally of the scopes relative to the spectacle lenses. This often creates a problem for low vision wearers who frequently have a need for remounting and refitting of the scope-lens device a second or third time in order to achieve wearer acceptability. This refitting is costly and time consuming because, in each event, a new "carrier lens" has to be constructed in order to move the scope mounting point to a different location laterally of the lens.
Another problem created when mounting a scope in a lens through-opening in such prior art systems is their requirement that the lens be custom bored and/or machined or to be a cemented substructure , and the lens utilized as a means of support. Such systems may also require special shaping of the lenses or frames, or are limited to the use of one specific design or shape of eyeglass frames and lenses. In addition, if the lens material needs to be bored to mount the scope, the lens material choice is limited, i.e., lens material which provides an acceptable degree of shatter resistance is difficult if not impossible to bore, at least in an economical manner.
Through-lens scope mounting is also disadvantageous when it is desired to align the scope axis at or near the optical center of the associated eyeglass lens. The minimum axial length of the through-lens opening needed to provide adequate cantilever mounting support results in the outer periphery of the lens being too thick to be acceptable when ground to meet high myoptic prescriptions.
Other problems associated with prior art telemicroscope-carrier lens combinations is their inability to implement needed cylindrical correction for astigmatic viewer correction since the scope lens system is not coupled in series with the carrier lens correction. Although theoretically it is possible to build such correction into the scope lenses, since every spectacle lens prescription is different, and if the spectacle prescription is substantial and correction for astigmatism is required, determination of implementation or deletion of spectacle prescription requirements should desirably be left completely to the qualified vision care specialist or certified low vision specialist who can prescribe and craft the necessary corrections in the spectacle lens independently of the scope lens system.
Another problem associated with microtelescopes in general is the need to direct the light effectively, to refract light and to make the highest and best possibly use of available light, while at the same time maintaining the widest possible field of vision. This parameter of a telemicroscope is often referred to as its "light gathering ability". Since no more light then enters the objective lens can effectively be refracted and exit the pupil lens, it is of the utmost importance that this light be reduced or dimensioned as little as possible prior to exit from the scope, either by the medium used for refraction or by any other internal device designed to redirect light or remedy ambient light reflection within the telemicroscope. In the aforementioned prior art Edwards '238 patent, this problem is approached by providing a diaphragm diameter based on an established ratio of tube length to thereby determine the necessary diaphragm diameter. This diaphragm diameter method, while eliminating a fair portion of ambient light reflection, does however decrease the field of view substantially, since it simply reduces the internal diameter of the tube to control the amount of light, thereby reducing the ambient light. Other prior art approaches to this problem include the use of a "dull black finish" on the internal surface of the device for the reduction of ambient light reflection, but this has not been as effective as desired in achieving reduction of ambient light reflection.